1. Field of the Invention
The present invention relates to a memory card usable as a prepaid card or the like and, more particularly, to a memory card including a nonvolatile semiconductor memory capable of being rewritten or initialized to be reused.
2. Description of the Related Art
It is a magnetic card that has been used conventionally as the main stream of a prepaid card. The magnetic card is constituted such that a magnetic substance is applied to part of one side of a card substrate of plastics or the like and data corresponding to the amount of prepaid money is magnetically recorded on the magnetic part of the card substrate. The magnetic card has the drawback wherein it is easy to be counterfeited because of simple structure and low cost for counterfeit, though its manufacturing cost is low. To eliminate the drawback, an IC memory card (simply referred to as a memory card hereinafter) mounted with an IC memory has recently been used as a prepaid card since the memory card is so high in cost for counterfeit that it cannot be counterfeited. In the memory card, a memory section (memory cell) for recording data is constituted of fuse memories incapable of being rewritten, and the amount of used money is counted and recorded by disconnection of the fuse memories.
However, if, in the above memory card, the prepaid money are completely spent, all the fuse memories are cut off, and the memory card has to be thrown away since it cannot be used any more. The memory card is therefore unfavorable for protection of resources and prevention of environmental pollution. Since, furthermore, the memory card cannot be reused, its own manufacturing cost is increased.
The fuse memories can be replaced with an EEPROM (Electrically Erasable Programmable ROM) in order to reuse the prepaid card. If, however, a rewrite operation is allowed without restriction, the following drawback occurs: In case a write command leaks out to a user, the user is likely to rewrite the EEPROM and to use the prepaid card without restriction.